High-Speed Receivers - Newport Corporation · microwave frequencies benefit from detectors with flat frequency responses and improved response at higher frequencies. These applications

U S E R ’ S G U I D E

High-Speed ReceiversModels 1591, 1592, 1580-A, 1544-A, 1580-B,

1544-B, 1484-A, and 1474-A

High-Speed DetectorsModels 1480-S, 1481-S, 1414,1004, 1014,

1444, and 1024

3635 Peterson Way • Santa Clara, CA 95054 • USAphone: (408) 980-5903 • fax: (408) 987-3178

e-mail: [email protected] • www.newfocus.com

Warranty

Newport Corporation guarantees its products to be free of defects for one year from the date of shipment. This is in lieu of all other guarantees, expressed or implied, and does not cover incidental or consequential loss.

Information in this document is subject to change without notice.

Copyright 2001-1998, 2013, Newport Corporation. All rights reserved.

The New Focus logo and symbol are registered trademarks of Newport Corporation.

Document Number 90063253 Rev. A

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Contents

Operation Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Photoreceivers (Amplified Photodiodes) . . . . . . . . . . . . . . . . . . 5 Photodetectors (Unamplified Photodiodes) . . . . . . . . . . . . . . . 6 Mechanical/Optical Description . . . . . . . . . . . . . . . . . . . . . . . . . . 7Handling Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Powering and Connecting the Photodector/Photoreceiver . . . . .10 Connecting the Power Supply and Bias Monitor . . . . . . . . . . 10 Battery Check For Units with Internal Batteries . . . . . . . . . . . 11 DC-coupled Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Connecting the Optical Input to the Receiver . . . . . . . . . . . . . 12

Troubleshooting Possible Problems and Solutions . . . . . . . . . . . . . . . . . . . . . . . . 13Checking the Dark Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Basic Optical Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

CharacteristicsSpecifications Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Customer ServiceTechnical Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Appendices1: Microwave Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242: Replacing the Battery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253: Difference between a time-domain-optimized detector and a frequency-domain-optimized detector . . . . . . . . . . . . . . . 254: DC-coupled Photoreceivers Crossover Region . . . . . . . . . 27

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5

Operation

Introduction

High-speed and ultrahigh-speed measurements of optical waveforms are easy with the New Focus photoreceiver/photodetector modules. These modules convert optical signals to electrical signals and can be used to provide every high-speed/high-frequency instrument in your lab an optical input. The small size of the modules allows you to connect them directly to your test instrument, amplifier if needed, or another high-speed component. This eliminates the need to follow the photoreceiver with coaxial cables, which can distort time-domain waveforms and attenuate CW microwave signals. The optical signal is delivered to the photodiode in the module through a single-mode or multimode optical fiber.

Photoreceivers (Amplified Photodiodes)For the photoreceiver models, the photodiode is followed by a low-noise, linear, high-bandwidth amplifier. This combines gain and low noise to reduce the input-referred noise floor of your system and maintains linearity at high output levels, providing a high dynamic range. The high output level also facilitates operation with logic circuits. The high-speed amplifier, which follows the photodiode, produces a clean impulse response with minimal ringing. This is ideal for digital communication measurements. Most receivers have a negative conversion gain due to the inverting amplifier used – if you are using an oscilloscope and would like to see a positive output, an inverting function can be used.

DC-coupledFor DC-coupled receivers, the DC coupling is achieved by summing the signal’s DC component with the high-speed

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AC component at the output of an AC-coupled high-speed transimpedance amplifier. The gain of the DC path is set equal to that of the AC path and temperature compensated so that extinction ratios may be accurately measured.

Photodetectors (Unamplified Photodiodes) Frequency Domain Optimized

Applications that rely on transmitting signals at RF and microwave frequencies benefit from detectors with flat frequency responses and improved response at higher frequencies. These applications include linear fiber-optic transmission to and from remote antennas for communication satellites, wireless cellular networks, and cable television. Since the time-domain response is not critical in these applications, the impulse response can have ringing. In particular, Models 1414 and 1014 detectors are frequency domain optimized to provide especially flat frequency responses over wide bandwidths.

Time Domain OptimizedIf you need accurate reproduction of your signal in the time domain, choose Model 1444 or 1024 time-domain-optimized detectors. These models provide clean, fast impulse responses with minimal ringing, and are ideal for pulse measurements with digital high-speed oscilloscopes. Moreover, they can be used in digital communications applications, where spurious ringing can degrade eye diagrams and the bit-error-rate (BER) measurement of your system. And, because these detectors are internally terminated at 50 Ω, you won’t have to worry about any reflections between the detector and filter for standardized BER testing with SDH and SONET filters.

Internal 9-V BatteryModels 1414, 1004, 1014, 1444, and 1024 combine an internal 9-V battery with the bias circuitry which make these self-contained, eliminating the need for an external power supply and reducing the possibility of photodiode damage due to overvoltage.

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Figure 1: Models 1591, 1592, 1580-B,

1544-B, and 1544-B-50

Bias Optical Input

Off On

Monitor

fiber-optic input connector (FC)

bias-monitor port (output =1 mV/µA)

AC-DCswitch

PWR

power indicator LED

Mechanical/Optical DescriptionA gold-plated microwave housing inside the module contains the high-frequency circuitry. This housing is bolted to a printed-circuit board which regulates the bias for the high frequency components and amplifies the DC photocurrent for the monitor port. The optical signal is brought from the front-panel connector to the microwave housing using the appropriate fiber. In models with single-mode fiber input, the optical signal is delivered to the PIN photodiode through a 0.1m, 9-um core optical fiber. For multimode input the signal is delivered through a 50-μm (or 62.5-μm) core graded-index multimode fiber of the same length. For 12 GHz models and faster, an internal lens focuses the light onto the small high-speed PIN photodiode. There is no degradation in frequency response since the fiber is ~0.1 m long. In modules with a battery, the fiber is protected by a sheet metal flange to prevent damage while replacing the battery.

New Focus offers several photodetectors and photoreceivers, allowing you to match the wavelength, bandwidth, and fiber type of your application.

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Bias ChkOff On Batt

Monitor



power switch

battery-check button

Optical Input

Figure 3: Models 1414,

1414-50, 1004, 1014, 1024,

1444, and 1444-50

BiasPWRMonitor1mV/µA



power indicator LED

Optical Input

Model 1474-A35 GHz IR Photoreceiver

Figure 4: Models 1484-A, 1484-A-50, and

1474-A

Figure 2: Models 1580-A,

1544-A, 1544-A-50,

1480-S, 1481-S, and 1481-S-50

Optical Input

Off On BattChk Bias

Monitor



power switch

positive supplycheck

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Handling PrecautionsThe detector is sensitive to electrostatic discharges and could be permanently damaged if subjected to even to small discharges. Whenever handling, make sure to follow these precautions:

• Follow standard electrostatic-discharge precautions, including grounding yourself prior to handling the detector or making connections—even small electrostatic discharges could permanently damage the detector. A ground strap provides the most effective grounding and minimizes the likelihood of electrostatic damage.

• Do not over-torque the microwave K-connector. Excessive torque can damage connectors.

• Make sure the optical connector is clean and undamaged before connecting it to the detector module.

3.15(80.1)

2.26(57.5)

2.00(50.8)

Output K-Connector

2.00(50.8)1.59

(40.3)

.54(13.6)

Power Connector

Figure 5: Side and back

view. (Note that the battery

operated modules will not have the

power connector on the side.)

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Powering and Connecting the Photoreceiver / PhotodetectorConnecting the Power Supply and Bias Monitor

1. Prior to handling the detector, ground yourself with a grounding strap to prevent electrostatic damage to the module.

2. Connect the power cable to your disabled power supply. Two power cables were included with the receiver; use the appropriate cable for your power supply.

Connecting to a New Focus 0901 power supply: Using the appropriate cable, connect one end of the cable to one of the power supply’s 300-mA outputs, and the other end to the module. If the 300-mA outputs are in use, the 300-mA banana-plug output can also be used with the appropriate cable. On older 0901’s, the 100-mA banana-plug output can provide enough current for certain models. Check the current rating for your specific model in the Power Requirements section of the specifications table.

Connecting to another power supply:Use the cable with the three-pin power connector on one end and three banana plugs on the other end. Be careful to connect the banana plugs to the power supply as follows; connect the red plug to a +15-V source; connect the black plug to a -15-V source; connect the green plug to the common or ground of the two sources. The +/- 15-V sources must be able to provide at least the required current for your specific model. Connect the three-pin power connector to the module.

3. Microwave Connection and Set-up

A. Connect the photoreceiver module’s K-connector to a test instrument or component that has a 50-Ohm input impedance. If necessary, use a high-frequency cable (best performance is achieved without a cable).

B. To avoid connector damage and signal distortion, be sure that the cable and the instrument you intend to

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connect to the module have compatible connectors. See “Appendix: Microwave Connectors”.

4. After connecting to the supply, enable or turn on the supply. While the module can handle any power-on sequence, it is recommended that both positive and negative be turned on together.

5. If desired, connect the Bias Monitor port to a voltmeter and observe the voltage level with no optical input. This dark voltage should be < 10 mV. Changes from the dark level will be proportional to photocurrent and will provide a low-frequency indication of signal strength.

If you are coupling light into a fiber, use the voltmeter to monitor the photocurrent to help optimize the coupling.

Battery Check For Units with Internal Batteries

1. Turn on power using the Off/On switch.

2. Connect a voltmeter to the Bias Monitor SMA connector.

3. Press the Batt Chk button. The voltage should be 3.5 to 5 V (-3.5 to -5 V for the 1004 detector).

4. When finished using the module, turn off power to preserve battery life.

DC-coupled Modules

The 1591, 1592, 1580-B, 1544-B, and the 1544-B-50 have a front panel switch to select either the DC- or AC-coupled electrical output. The DC-coupled mode is indicated by a red light while the AC-coupled mode is indicated by a green light.

Connecting the Optical Input to the Receiver

Be aware that if your fiber is multimode at the operation wavelength then excessive fiber length can lead to signal distortion. If you have the multimode “-50” model, use 50/125-μm graded index fiber. If you have model 1591,

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1592, 1580-A, or 1580-B use 62.5/125-μm graded index fiber. Smaller core fibers (including singlemode) will also work well.

1. Before connecting to the photoreceiver, verify the power in the fiber is within the safe operating range.

2. Make sure the fiber is clean and undamaged, then connect the fiber-optic cable to the module’s input.

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Troubleshooting

Possible Problems and Solutions

1. Low Gain:

Verify that the power supply has sufficient voltage and current capability.

If your output signal is lower than expected, a dirty input fiber may be causing the problem. See “Basic Optical Test” below and verify that the input fiber is clean.

The photodiode can be damaged by electrostatic discharge or excessive optical power, which leads to an increased dark voltage. A damaged photodiode can result in excess leakage current, lower responsivity, or a slower frequency/impulse response. See “Checking the Dark Voltage,” below. A damaged photodiode must be replaced by New Focus.

Severe mechanical shock may misalign the optics and lower the responsivity. See “Basic Optical Test” below. If dirty fiber tips have been ruled out, then the module must be repaired by New Focus.

2. Slow Response:


If the frequency or time domain response is slower than expected, then most likely the photodiode or amplifier is damaged. See “Checking the Dark Voltage,” below. A damaged photodiode must be replaced by New Focus. If the dark voltage is okay, then the problem is most likely a damaged amplifier and the module must be repaired by New Focus.

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Severe mechanical shock may misalign the optics. If the frequency response drops excessively from a low frequency up to several gigahertz (or if the time response has a slow component) then misalignment is a possibility and the module must be repaired by New Focus.

3. Little or No Response:


After ruling out a dirty or defective fiber and making sure there is no loss due mismatch of input fiber core diameter, a damaged component is the most likely cause. The module must be repaired by New Focus.

For assistance in troubleshooting or arranging for a repair, please see the “Customer Service” section of this manual.

Checking the Dark Voltage

1. With no light entering the module, turn on power to the detector.

2. Use a voltmeter to measure the Bias Monitor output voltage. This voltage is the dark voltage.

3. If the dark voltage is >10 mV, then the photodiode may be damaged and may need to be repaired by New Focus. It is possible the module will still operate well with a voltage only somewhat higher than 10 mV. The user may wish to continue using the module and monitor this voltage to see if it degrades.

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Basic Optical Test

To quickly test your receiver, run this simple optical test.

1. Turn the receiver on.

2. Using a voltmeter or oscilloscope, measure the output voltage from the Bias Monitor on the front panel of the module. With no light input, the Bias Monitor voltage should be <10 mV.

3. Illuminate the photodetector.

4. With the voltmeter or oscilloscope, you should observe a DC output voltage. If you know the optical power and wavelength, you can calculate the expected output voltage (Vout) using the expression:

Vout = Pin • R • G ,

where Pin is the input optical power (Watts), R is the photodiode’s responsivity (A/W) found on the datasheet shipped with the unit and G is the Bias Monitor’s transimpedance gain, 1 V/mA. If the measured voltage is substantially less than expected, the module may need to be returned to New Focus for repair.

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Specifications5-GHz Photoreceivers .......................................................................................1591, 1592 ...................................................Table 112-GHz Optical Photoreceivers ...........................................................1580-A, 1544-A .............................................Table 212-GHz DC-coupled Photoreceivers ..............................................1580-B, 1544-B .............................................Table 322-GHz Photoreceivers ........................................................................................1484-A ........................................................Table 438-GHz Photoreceivers .........................................................................................1474-A ........................................................Table 415-GHz Photodetectors .......................................................................................1480-S ........................................................Table 525-GHz Photodetectors ...............................................................................1481-S, 1414 ................................................Table 540-GHz Photodetectors .......................................................................................... 1004 ...........................................................Table 645-GHz Photodetectors .......................................................................................... 1014 ...........................................................Table 618-ps Photodetectors ................................................................................................ 1444 ...........................................................Table 712-ps Photodetector ................................................................................................... 1024 ...........................................................Table 7Characteristics (typical, except as noted)

5-GHz Photoreceivers

Model 1591 1592

Wavelength Range nm 450-870 950-1630

Bandwidth, 3-dB (DC coupled), typ/min

GHz DC to 5.5 / 4.5 DC to 5 / 4.5

Low-Frequency Cutoff (AC coupled)

kHz 10 10

Risetime, 10-90% ps 80 85

Conversion Gain2, typ/min V/W 600 / 500 1300 / 1100

NEP 2 pW/rt(Hz) 37 17

Output Noise mVrms 1.8 1.8

Saturation Power2 mW 2.2 1

Maximum Safe Input,2,5 mW 5.5 2.5

Output Impedance Ohm 50 50

Bias-Monitor Gain V/mA 1 1

Bias-Monitor Bandwidth kHz 50 50

Bias-Monitor Output Impedance

Ohm 10k 10k

Power Requirements6 +/-15 V, 150 mA +/-15 V, 150 mA

Detector Type GaAs InGaAs

Output Connector Anritsu K Anritsu K

Input Connector FC/PC FC/PC

Input Fiber 62.5-μm MM 62.5-μm MM

Operating Temperature, min/max

°C 10/35 10/35

Table 1

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12-GHz Fiber Optic Photoreceivers

Model 1580-A 1544-A 1544-A-50

Wavelength Range nm 780-870 500-1630 780-16301

Bandwidth, 3-dB, typ / min

GHz 12 / 10.5 12 / 10.5 12 / 10.5

Low-Frequency Cutoff

kHz 10 10 10

Risetime, 10-90% ps 32 32 32

Conversion Gain2, typ / max

V/W -550 / -450 -900 / -800 -800 / -700

NEP2 pW/rt(Hz) 42 24 27

Output Noise mVrms 2.9 2.8 2.8

Saturation Power2 mW 1.5 0.7 0.7

Maximum Safe Input,2,5 mW 3 2 2

Output Impedance Ohm 50 50 50

Bias-Monitor Gain V/mA 1 1 1

Bias-Monitor Bandwidth

kHz 50 50 50


Ohm 10k 10k 10k

Power Requirements6

+/-15 V, 200 mA

+/-15 V, 200 mA

+/-15 V, 200 mA

Detector Type GaAs InGaAs InGaAs

Output Connector Anritsu K Anritsu K Anritsu K

Input Connector FC/PC FC/PC FC/PC

Input Fiber 62.5-μm MM SM 50-μm MM


°C 10/35 10/35 10/35

Table 2

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12-GHz DC-coupled Photoreceivers

Model 1580-B 1544-B 1544-B-50


Bandwidth, 3-dB (DC coupled) , typ / min

GHzDC to

12 / 10.5DC to

12 / 10.5DC to

12 / 10.5

Low-Frequency Cutoff (AC coupled)

kHz 10 10 10

Risetime, 10-90% ps 32 32 32

Conversion Gain2, typ/max

V/W -550 / -450 -900 / -800 -800 / -700

NEP2 pW/rt(Hz) 42 24 27

Output Noise mVrms 2.9 2.8 2.8

Saturation Power2 mW 1.5 0.7 0.7





kHz 50 50 50


Ohm 10k 10k 10k

Power Requirements6

+/-15 V, 200 mA

+/-15 V, 200 mA

+/-15 V, 200 mA

Detector Type GaAs InGaAs InGaAs



Input Fiber 62.5-μm MM SM 50-μm MM

Operating Temperature,min/max

°C 10 / 35 10 / 35 10 / 35

Table 3

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22 and 38-GHz Photoreceivers

Model 1484-A 1484-A-50 1474-A


Bandwidth, 3-dB, typ / min

GHz 22/20 22/20 38/35

Low-Frequency Cutoff

kHz 15 15 15

Risetime, 10-90% ps 16.5 16.5 12.5

Conversion Gain2, typ / max

V/W -80 / -70 -75 / -65 -75 / -65

NEP2 pW/rt(Hz) 36 38 38

Output Noise3 μVrms 590 590 590

Output Voltage4 V -0.6 -0.6 -0.6





kHz 15 15 15


Ohm 10k 10k 10k

Power Requirements+/-12 to +/-15V,100 mA

+/-12 to +/-15V,100 mA

+/-12 to +/-15V,100 mA



Input Fiber SM 50-μm SM


°C 10/35 10/35 10/35

Table 4

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15- and 25-GHz Photodetectors

Model 1480-S 1481-S 1481-S-50 1414 1414-50

Wavelength Range

nm 400-870 400-8701 750-870 500-1630 850-16301

Bandwidth, 3-dB, typ/min

GHz 15 / 13 25 / 22 25 / 22 25 25

Risetime, 10-90%

ps 25 15 15 14 14

Conversion Gain2 typ/min

V/W 11/10 11/10 9/8 17/15 14/12

Responsivity2 A/W 0.5 0.5 0.36 0.7 0.6

Saturation Power2 mW 2 2 2 2 2

Maximum Safe Input,2,5 mW 5 5 5 10 10

Output Impedance

Ohm 50 50 50 50 50

Bias-Monitor Gain

V/mA

1 1 1 1 1


kHz 50 50 50 50 50


Ohm 10k 10k 10k 1k 1k

Power Requirements6

+/-15 V, 200 mA

+/-15 V, 200 mA

+/-15 V, 200 mA

Internal 9-V Battery


Detector Type GaAs GaAs GaAs InGaAs InGaAs

Output Connector

Anritsu K Anritsu K Anritsu K Anritsu K Anritsu K

Input Connector

FC/PC FC/PC FC/PC FC/PC FC/PC

Input Fiber62.5-μm

MMSM

50-μm MM

SM 50-μm MM

Operating Temperature,min/max

°C 10 / 35 10 / 35 10 / 35 10 / 35 10 / 35

Table 5

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40- and 45-GHz Photodetectors

Model 1004 1014

Wavelength Range nm 400-870 500-1630

Bandwidth, 3-dB, typ/min GHz 40 / 35 45 / 40

Risetime, 10-90% ps 9 9

Conversion Gain typ/min2 V/W 6.6 typ 11/9

Peak Responsivity A/W 0.2 0.45

Saturation Power mW 5 2

Maximum Safe Input5 mW 10 5

Output Impedance Ohm 100 50

Bias-Monitor Gain V/mA 1 1

Bias-Monitor Bandwidth kHz 50 50


Ohm 1k 1k

Power RequirementsInternal 9-V

BatteryInternal 9-V

Battery

Detector Type GaAs InGaAs

Output Connector Anritsu K Anritsu K

Input Connector FC/PC FC/PC

Input Fiber SM SM


°C 10/35 10/35

Table 6

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1 Lens dispersion limits wavelength range.2 At 1550 nm for InGaAs Models and 775nm for GaAs models. For GaAs models,

response at 850nm will be similar. 3 DC - 50 GHz; noise bandwidth is ~42 GHz for each model.4 5% compression of impulse response.5 CW, or average power with high-speed modulation.6 Model 0901 recommended.

12- and 18.5-ps Photodetectors

Model 1444 1444-50 1024


FWHM, Impulse Response typ/max

ps 16.5/18.5 16.5/18.5 11/12

Bandwidth, 3-dB, GHz 20 20 26

Conversion Gain2

typ/minV/W 17/15 14/12 11/9

Responsivity2 A/W 0.7 0.6 0.45

Saturation Power2 mW 2 2 2



Bias-Monitor GainV/mA

1 1 1


kHz 50 50 50


Ohm 1k 1k 1k

Power Requirements




Detector Type InGaAs InGaAs InGaAs



Input Fiber SM 50-μm MM SM


°C 10 / 35 10 / 35 10 / 35

Table 7

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Customer Service

Technical SupportInformation and advice about the operaion of any New Focus product is availabe from our applications engineers. For quickest response, ask for “Technical Support” and know the model number and serial number for your product.

Hours: 8:00–5:00 PST, Monday through Friday (excluding holidays).

Toll Free: 1-877-835-9620 (from the USA & Canada only)

Phone: (408) 980-4330

Support is also available by fax and email:

Fax: (408) 919-6083

Email: [email protected]

We typically respond to faxes and email within one business day.

ServiceIn the event that your photoreceiver malfunctions or becomes damaged, please contact New Focus for a return authorization number and instructions on shipping the unit back for evaluation and repair.

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Appendices

Appendix 1: Microwave Connectors

The performance you obtain when making high-speed measurements depends in part on the instruments you use and how connections are made to the instruments. Connect the male connector of the photoreceiver directly to the female connector of the instrument. If you need to use an adapter, make sure it is designed for your frequency range of interest. The following table lists common connectors, their upper frequency limit, and mating compatibility. If you use an intervening coaxial cable, select a shorter cable to minimize loss and verify that its bandwidth rating is sufficient. For more information please see the Optical Measurement section in the Application Notes selection guide on the Newport webpage. In particular, Application Note 1: Insights into High-Speed Detectors and High Frequency Techniques.

Connector Type Frequency Limit, GHz Compatibility

BNC 4 -

SMA 18 or 26.5 3.5 mm, K

3.5 mm 34 SMA, K

K (2.92 mm) 40 SMA, 3.5

2.4 mm 50 V

V (1.85 mm) 65 2.4 mm

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Appendix 2: Replacing the Battery

1. Turn off the module and remove the two screws on the back panel with a Phillips screwdriver.

2. Remove the back panel and replace the battery.

3. Replace the back panel.

4. Check the battery level as described above in the “Battery Check” section.

Appendix 3: Difference between a time-domain-optimized detector and a frequency-domain-optimized detector

Circuitry in frequency-domain-optimized detectors is designed to produce a flat frequency response, where the responsivity varies only slightly across the operating bandwidth. Time-domain-optimized detectors, in contrast, produce clean, ring-free pulses. By using Fourier-transform methods, you can show that clean ring-free pulses result in a characteristic roll-off in the frequency domain. On the other hand, a flat frequency response results in some controlled ringing in the impulse response.

–40

–30

–20

–10

0

10

Frequency

Resp

onse

, dB A

B

Figure 7. Frequency-Domain vs. Time-Domain: (A) Detectors designed for flat frequency response have enhanced responsivities at high frequencies. (B) Detectors that are optimized for clean, ring-free pulses show a characteristic drop off in 3-dB frequency response.

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–0.4

–0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Time

Ampl

itude

, a.u

.

Figure 8. Time-Domain Optimized: This is the impulse response of a detector that is optimized for the time domain. You can see the characteristic frequency response in the figure above.

–0.4

–0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Time

Ampl

itude

, a.u

.

Figure 9. Frequency-Domain Optimized: This is the impulse response of a detector that is optimized for a flat frequency response. You can see the corresponding frequency response in figure above.

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Appendix 4: DC-coupled Photoreceivers Crossover Region

In looking at the frequency response of the DC-coupled receivers, a “crossover” region exists where the DC response rolls off and the AC response rises. In this region, near 25kHz, the response is not flat. Signals with significant energy in this region will be somewhat distorted. A time-domain example is seen in Figure 10 which shows the response for a long-duration step input. For most applications, such as measurement of extinction ratios on gigabit-per-second waveforms, the crossover will be insignificant.

Figure 10. Example crossover behavior for DC-coupled receivers.

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Documents

High-Speed Receivers - Newport Corporation · microwave frequencies benefit from detectors with flat frequency responses and improved response at higher frequencies. These applications